1. Field of the Invention
The present invention relates to flash memory devices, and more particularly, to a method of controlling a copy-back operation of a flash memory device.
2. Discussion of Related Art
In general, a flash memory device includes a page buffer for programming or reading a large quantity of data for a short period of time. Accordingly, the program or read operation of the flash memory device is executed by the page buffer on a page by page basis.
Recently, to further improve the degree of integration of the flash memory device, a flash memory device including Multi-Level Cells (MLCs) capable of storing plural bits of data has been developed. In general, since 2-bit data can be programmed into a MLC, one MLC can store any one of four data values, i.e., [11], [10], [00] and [01]. The MLC has a threshold voltage (one of Vt1 to Vt4) corresponding to the stored data (one of [11], [10], [00] and [01]).
A memory cell capable of storing single bit data is generally referred to as a Single Level Cell (SLC). A flash memory device including these SLCs basically supports the copy-back operation.
The copy-back operation includes storing data, which are stored in memory cells of a source page (i.e., one address), in a page buffer, and programming the stored data (without or with change) into memory cells of a target page (i.e., the other address). However, a flash memory device including the MLCs does not support the copy-back operation.
Accordingly, in the flash memory device including the MLCs, one method of copying data of a source page to a desired target page is to read the data from the source page, store the read data in a storage unit external to a flash memory chip and then program the stored data into the target page. Another method is to read the data from the source page, store the read data in a storage space within a chip and then program the stored data in the target page.
However, these methods are problematic in that they are ineffective since additional storage spaces other than the page buffer are required and a programming time of the target page is long. In addition, if the additional storage space is disposed within the flash memory device, a problem arises because the size of the flash memory device is increased.